Transceiver integrated circuit
STS-12/STM-4, STS-3/STM-1 | XRT91L30 EXAR

The XRT91L30 is a fully integrated SONET/SDH transceiver for SONET/SDH 622.08 Mbps STS-12/STM-4 or 155.52 Mbps STS-3/STM-1 applications. The transceiver includes an on-chip Clock Multiplier Unit (CMU), which uses a high frequency Phase-Locked Loop (PLL) to generate the high-speed transmit serial clock from a slower external clock reference. It also provides Clock and Data Recovery (CDR) function by synchronizing its on-chip Voltage Controlled Oscillator (VCO) to the incoming serial data stream. The internal CDR unit can be disabled and bypassed in lieu of an externally recovered received clock from the optical module. Either the internally recovered clock or the externally recovered clock can be used for loop timing applications. The chip provides serial-to-parallel and parallel-to-serial converters using an 8-bit wide LVTTL system interface in both receive and transmit directions.

The transmit section includes an 8x9 Elastic Buffer (FIFO) to absorb any phase differences between the transmitter clock input and the internally generated transmitter reference clock. In the event of an overflow, the FIFO can automatically recover from an overflow condition. The device can monitor Loss of Signal (LOS) condition and automatically mute received data upon LOS. An on-chip SONET/SDH frame byte and boundary detector and frame pulse generator offers the ability recover SONET/SDH framing and to byte align the receive serial data stream into the 8-bit parallel bus.